HIGH-RESOLUTION TRANSMISSION ELECTRON MICROSCOPY OF POLYMER CRYSTALS

Abstract

High-resolution electron microscopic (HREM) observation with a transmission electron microscope (TEM) is a powerful experimental method to clarify complicated fine structures, if specimens can endure electron irradiation. Though polymer crystals are very sensitive to electron irradiation, it has turned out possible to observe them by high-resolution electron microscopy at molecular dimensions. If we perform our experiment carefully enough, the resolution limit predicted from the durability against radiation damage can be achieved even for the polymer crystals. One should recognize that HREM images are composed of lattice fringes which are formed by the interference between unscattered and scattered electron waves. Several factors determining performance of the TEM itself should be known. Then the optical systems of the TEM must be aligned carefully and they must be stabilized before taking HREM images. Photographic films are still the best medium to record HREM images. In HREM observation of polymer crystals, reducing the total amount of electron dose given to the specimen before taking an HREM photograph is the most important. A low-dose function which can focus the specimen at a position remote from the region to be photographed in the specimen is useful to reduce the radiation damage during focusing. The condition to record an HREM image is determined by the durability of each specimen against radiation damage. The method to increase the durability of a specimen to electron irradiation by cooling can improve the resolution limit of the specimen. HREM observation of the β-form single crystals of syndiotactic polystyrene is an example. Arrangement of molecular stems both in the solution-grown single crystal and in the melt-grown one was revealed by the HREM observation.